The active carbon is used in a wide variety of processes as an adsorbent, a catalyst, a support or the like. That is, the active carbon is widely used not only as a catalyst but also as a support which carries thereon a catalytic component for reactions such as the ortho-para hydrogen conversion, the halogenation or dehalogenation or the oxidation.
A large number of catalysts comprising an active carbon as a support are known, which include catalysts for vinyl acetate production, halogenation or dehalogenation, oxidation reduction and olefin polymerization. Specifically, for example, a catalyst comprising zinc acetate supported on an active carbon has been used for the production of vinyl acetate from acetylene and acetic acid (Sekiyu Gakkaishi (Journal of Petroleum Institute of Japan), Vol. 29, No. 2, (1986)). Further, various catalysts have been proposed for the vapor phase reaction of oxygen, carbon monoxide and an alcohol to produce a carbonic acid diester, which include a catalyst prepared from an active carbon impregnated with a metal halide or a mixed metal halide (Published Japanese Translation of PCT Patent Applications from Other States, No. 503460/1988) and a catalyst comprising a catalytic component such as copper chloride supported on active carbon obtained from a vegetable or polymer raw material (Japanese Patent Laid-open Publication No. 6(1994)-239795). Further a catalyst comprising a platinum group metal chloride and for example a bismuth compound supported on active carbon has been proposed to be used for the vapor-phase catalytic reaction of carbon monoxide and an alkyl nitrite to produce a carbonic acid diester (Japanese Patent Laid-open Publication No. 4(1992)-89458).
The above reactions are generally exothermic. It is preferred that the exothermic vapor-phase reaction is conducted in the fluidized bed reactor capable of effectively removing heat. Even when the reaction proceeds endothermically, the fluidized bed reactor is preferred because of its effective heat transfer. For efficiently carrying out the reaction in the fluidized bed reactor, it is preferred to use a granular catalyst which is excellent in not only catalytic activity but also mechanical strength and attrition resistance and which has a controlled particle size and uniform bulk density. Especially, a granular catalyst having a controlled small particle size may enable attainment of more efficient heat transfer, a well-controlled reaction conditions and easy scale up of the vapor-phase fluidized bed reactor.
However, the active carbon (granular active carbon) is brittle and is easily attrited, so that, it has been desired for the granulated active carbon used as a catalyst for the fluidized bed or a catalyst support to be improved in the mechanical strength and attrition resistance.
Further, the granulated active carbon obtained by conventional methods generally has a relatively large particle size, and it has been difficult to prepare a granulated active carbon whose particle size is less than 300 .mu.m.
Proposals have also been made for active carbon supports having improved attrition resistance and mechanical strength. For example, Japanese Patent Laid-open Publication Nos. 3(1991)-193616 and 4(1992)-154611 disclose granulated active carbons of high strength which are obtained by milling active carbon powder, bentonite clay and a phosphorus compound or boron compound in specified proportions and granulating followed by calcination. However, the granulated active carbons obtained by the methods of the above publications have a size of, for example, about 4.5 mm in diameter and 6 mm in length and even after pulverization, have a size of about 0.59 to 2.38 mm. Thus, any granulated active carbon having a particle size which is suitable for a catalyst for fluidized bed has not been obtained.
Japanese Patent Laid-open Publication No. 54(1979)-85194 discloses an attrition-resistant active carbon support (or active carbon catalyst) produced by impregnating an attrition-resistant support material with an aqueous solution of saccharide, drying and pyrolizing the saccharide in the absence of air to carbonaceous substance to thereby cover the surface of the support material with active carbon. This publication reports that when SiO.sub.2 or Al.sub.2 O.sub.3 of 35 to 130 .mu.m in average particle size obtained by spray drying is used as a support material, solid particles covered with active carbon having the same average particle size are obtained.
The inventors have made extensive and intensive studies with respect to active carbon which is excellent in attrition resistance and which has a small particle size for fluidized bed. As a result, it has been found that a process, comprising spray drying a slurry containing an active carbon or a precursor thereof and an attrition-resistant inorganic substance or a precursor thereof so as to obtain particles having an average size of smaller than 300 .mu.m; and calcining the particles, can provide solid particles which comprise a substantially homogeneous mixture of the active carbon and the attrition-resistant inorganic substance, which have an average particle size of smaller than 300 .mu.m and which are excellent in mechanical strength and attrition resistance.